The present invention relates to a control for an air distribution unit for delivering conditioned air into an area or space. More particularly, it relates to a control for maintaining the flow of conditioned air into the area at a minimum predetermined rate irrespective of the temperature requirements of the space and is an improvement over commonly assigned U.S. Pat. No. 4,120,453.
In the arrangement disclosed in U.S. Pat. No. 4,120,453, a first pressure signal is supplied to a 3-way valve from a first pressure regulator which is controlled by a bleed-type thermostat so that the first pressure signal represents the cooling demand. A second pressure signal is supplied to the 3-way valve from a second pressure regulator and represents the minimum quantity of air for adequate ventilation. The output of the 3-way valve is supplied to a bellows which coacts with cutoff plates to regulate air flow from the plenum. The output of the 3-way valve is controlled by a differential pressure valve which receives the first pressure signal from the first pressure regulator and plenum pressure to cause the 3-way valve to communicate either the first or second pressure signal to the bellows, as required.